This invention relates to an ultrasonic atomizing device or element such as an atomizer horn or a front driver. The atomizing device is operatively connected to an ultrasonic frequency generator for atomizing liquid fed to the device.
High power ultrasonic transducers have been employed in atomization of liquids for many years. In practice, the motion of a piezoelectric or magnetostrictive transducer is amplified either by the shape of the transducer itself or by the addition of a mechanical velocity transformer (so-called "horn") which is mechanically attached to its front driver. Liquid is brought into contact with the free or distal end of the vibratory element whereupon the oscillatory motion of the surface breaks the fluid into small droplets. The natural motion of the transducer/horn surface will impart a small velocity to the drop, thereby causing the droplets to form a fog which moves away from the surface slowly. Examples are found in U.S. Pat. Nos. 3,214,101, 4,153,201, 4,301,968 and 4,337,896.
In some ultrasonic atomizing devices known to the art, a gas moving device is employed to cause a gas stream to capture the fog and direct it in a certain direction at a higher rate of speed, as disclosed in U.S. Pat. No. 3,275,059. Devices such as these have been employed to atomize fuel for a combustion process, coat surfaces with a fine layer of material, nebulize drops of medicine into an airstream for treating bronchial distress, as well as for many other scientific and commercial applications well documented in the art.
Most of the known applications require a device to create droplets from a liquid stream and direct the resulting fog axially forward away from the transducer itself. To accomplish this, either the liquid feed to the transducer/horn face is via a concentric channel or passageway through the transducer and/or horn or the liquid feed enters the device at the nodal point of the transducer/horn perpendicularly to the long axis and intersects the axial feed hole, which is brought forward to the radiating face, as disclosed in U.S. Pat. No. 3,400,892. In another embodiment, the liquid feed is separate from the vibratory elements and takes the form of a sheath or feed tube having an outlet disposed to allow the liquid to drip or flow onto the radiating face of the transducer externally. Once the liquid contacts the radiating face of the device, the liquid is broken into droplets in the conventional manner. Such techniques are disclosed in U.S. Pat. Nos. 4,726,524 and 4,726,525.
The shape of the radiating face of an ultrasonic probe plays an important role in both the droplet size and spray pattern generated. However, all conventional probes either yield a spray pattern which is directed axially forward of the device and/or incorporate external liquid passageways in lieu of internal fluid guide channels.
Certain applications exist wherein devices known to the art would not be suitable for employment as a liquid atomizer. Examples of such applications are those which require a spray pattern which is radial with respect to the transducer/horn centerline and require a very thin or narrow horn due to the physical constraints of the system, thereby negating the possibility of using an external feed tube or sheath. Such applications would include the precision application of liquid reagents onto the interior side surfaces of a glass or plastic test tube or for coating the interior surfaces of a small diameter metal tubing with paint, anti-corrosive coating or magnetic media. In all of these cases, the spray pattern must be radially dispersed into very fine droplets. In some cases, the droplets must have an acceleration which has a vector pointed rearward, toward the transducer/horn itself. This would be necessary in cases where the dose of liquid to be atomized must be deposited upon the sidewall, thereby generally not allowing any of the material to contact the bottom surface of the test tube.